Hi there. Glad you got your sump fixed. As for the LFS
who told you that you loose bacteria after 20 mins is deeply incorrect. The BB is located on and in the substrates of your aquarium (sand, rock etc). Hardly any BB is in the water column.
Your DT should be fine for a few days/weeks assuming your rock and sand are in there? Since your skimmer is not currently on, I would keep an eye on the nitrates and phosphates in your tank. You can do large PWCs as needed.
Your DT will survive without your sump for some time as long as you keep an eye on it. Good luck!